The present invention relates to a new and improved method of, and apparatus for, fabricating workpieces, especially steering segments, for transmissions having a variable transmission ratio.
More specifically, the invention relates to a novel gear cutting machine and generating method for producing variable-ratio gearing, wherein between the workpiece and a gear cutter or hob there occurs a part-generating or rolling movement composed of a generating rotation about the workpiece axis and a generating displacement transverse to the workpiece axis as well as a to-and-fro cutting movement along the workpiece axis. Further, there is produced an additional or supplementary movement, controlled by a template, this additional movement being directed transversely with respect to the workpiece axis and altering the course of the generating curve of the workpiece.
With a state-of-the-art gear cutting machine of this type, as disclosed for instance in German Pat. No. 1,950,959, the additional or supplementary movement which is controlled by the template comprises a linear movement which occurs in or opposite to the direction of the generating displacement and which is superimposed upon such generating displacement and like the same is carried out by a generating slide or carriage together with a workpiece table mounted rotatably thereon for rotation about the workpiece axis. The inert mass of the generating slide or carriage together with the workpiece table and the workpiece is appreciable, and therefore it is difficult to accomplish the additional movement with an accuracy corresponding to the present day requirements of gear tooth systems, for instance for the steering transmissions of motor vehicles. This additional or supplementary motion is required in order to achieve a desired change of the course of the generating curve of the workpiece. By virtue of such difficulty the machining speed of the heretofore known gear hobbing machines must be limited in order that the unfavourable effect of the aforementioned inert masses upon the machining accuracy remains within acceptable limits. Consequently, limiting the machining or work speed constitutes an emergency solution, especially when machining workpieces, which like steering segments for motor vehicles, are fabricated in large numbers.